1975 AMPEG SVT
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1975 SVT characteristics: Squared "blackline" silkscreened graphics, two channels, small black D shaft knobs with silver tops, black plastic tone adjustment rocker switches, two metal power switches, small round red power light, silver grille cloth with plastic badge logo, preamp mounted underneath box top, non exposed fan, three prong power cord and outlet, fuse, Magnavox manufacturing, serial number stickers on the back panel right side and inside the box, four metal cord wraps, black painted chassis, (3) black transformers: power, filament and output, 6550 power tubes, circuit boards, capacitors, vinyl handles, vinyl covering over black painted wooden box, tube chart sticker, manila envelope containing schematic, six rubber feet, eight chassis connector bolts, "tilt back" 8x10 inch speaker cabinet with "towel bar" handle.
Ampeg serial number dating is undocumented and very difficult. Some examples of 1975 SVT serial numbers are 2662x, 4904x, 5687x, 6941x and 7278x. For more precise dating cross reference the serial number with the amplifier's transformer, potentiometer, capacitor and speaker codes.
Component code dating vintage SVT's: As with all vintage gear, the manufacture date is determined by the newest component/date stamp on the unit. On vintage SVT's, the newest date code on the unit is usually the four digit white ink stamp on the large output transformer. The first two numbers indicate the year, the third and fourth numbers indicate the production week of that year. Example: 7506 means a transformer made in the 6th week of 1975.
Other codes to determine the manufacture date: The other large power transformer and the adjacent smaller filament transformer should both have six digit codes stamped into the metal. The first three digits indicate the company's personal manufacturing code. Those should be 682, which indicate the Electrical Windings Company. The fourth number indicates the year. The fifth and sixth numbers indicate which week of that year.
Potentiometers are also date encoded. There is a seven digit code stamped into the metal. The first three digits indicate the company's personal manufacturing code. Those should be 137, which indicate Chicago Telephone Supply or CTS. The fourth and fifth numbers indicate the year. The sixth and seventh numbers indicate which week of that year. Capacitors and speakers can also be dated in a similar manner.